Modular wind turbine transmission

ABSTRACT

A wind turbine gear unit has a low speed gear module and a plurality of high speed gear modules wherein the low speed gear module is operable simultaneously to transmit torque to each of the high speed gear modules.

This invention relates to a wind turbine gear unit and in particular,but not exclusively, to an integrated rotor bearing wind turbine gearunit for multiple generators.

Torque transmission gear units for large multi-megawatt wind turbinescurrently face a range of design challenges. They have to be able totransmit the rotor power reliably, yet weigh as little as possible, costas little as possible and be designed in such a way as to allow easyrepair when required. Serviceability of the gearbox in the nacelle isvery important in these large units because it is very costly to removethem, especially from offshore sites, to be repaired elsewhere. Whenserviceable in the nacelle, the design must be such as to reducedowntime to a minimum.

Another important design consideration is integration, implying that thegear unit must aim to take over as many structural tasks from thetraditional wind turbine housing as possible. This means lower costs andlower overall weight. Furthermore the gear unit must be designed ascompactly as possible, as this would again be beneficial for cost andweight.

In accordance with one aspect the present invention provides a windturbine gear unit comprising a low speed gear module and a plurality ofhigh speed gear modules wherein said low speed gear module is operablesimultaneously to transmit torque to each of said high speed gearmodules.

At least one of said high speed gear modules may be a multi-stage gearunit and said low speed gear module may be a multi-stage gear unit.

The gear unit(s) described below address the above issues and otherissues by virtue of utilising:

-   -   i) Integrated rotor bearings.    -   ii) Modular design, mechanically and electrically.    -   iii) Multiple (small) generators.    -   iv) Gearbox housing used to transmit rotor loads to tower.    -   v) Absence of troublesome HSS (high speed shaft) couplings with        generator(s)

Further aspects of the present invention will become apparent from thefollowing description, given by way of example only, of embodiments ofthe invention in conjunction with the accompanying drawings in which:-

FIG. 1 shows a schematic diagram of a wind turbine gear unit accordingto the present invention; and

FIGS. 2 and 3 show in more detail variants of the invention.

In FIG. 1 a wind turbine rotor assembly (1) is coupled to the low speedgear element (2) of the gearbox, which may be either a bull gear or aring wheel. The rotor is supported on an integrated bearing/bearings (4)which also locate the low speed gear in the gear housing (5). When usinga ring wheel as the low speed gear element the bearing(s) (4) can forinstance be situated on the outer diameter of the ring wheel.

The low speed gear drives several individual single or multiple stagelow speed gear units (7) that may be comprised of planetary units,helical units or a combination of both. The secondary gear drive units(7) in turn drive several individual or multiple stage gear high speedgear units (8) that may be integrated or coupled to the generators (9).

The concept of the present invention may be characterised by:-

-   -   Power split to multiple generators. Rotor power is split in the        first low speed stage resulting in completely independent        mechanical torque transmission paths to the different        generators.    -   Modularity—Several modules can be identified:        -   A) The gearbox housing which doubles as a structural element            that transfers the rotor forces and bending moments to the            nacelle frame structure.        -   B) Low speed module consisting of either a ring wheel or            bull wheel supported on a bearing or bearings, coupled to            several pinions that may drive single or multiple low speed            stages.        -   C) High speed module consisting of one or more helical or            planetary stages (or a combination of both),and a generator.            The high-speed modules could be identical to one another but            do not have to be. Furthermore the generator can be            integrated with the final high-speed stage or flanged onto            the high-speed stage housing.    -   A control system allowing operation of the wind turbine without        one or more generators.    -   Operation of the Wind turbine may be continued with one or more        of the high-speed modules removed.    -   Disassembly in the nacelle: All modules are removable but the        main gearbox housing can be left in place to fulfil its        structural role even when the turbine is not operational. The        housing can be integrated with the base plate of the nacelle        (6).

FIGS. 2 and 3 show in more detail examples of possible practicalexecutions of the system described above. (Note: Underlined item numbersrefer to equivalent areas or items in FIG. 1)

In the construction shown in FIG. 2 the wind turbine rotor is attachedto the low speed shaft (1), which turns the low speed wheel (2) anddrives several pinion shafts (3). The low speed shaft is supported ontwo main bearings, (4) and (5), which also act as the rotor bearings.

The pinion shafts are supported by two bearings (6,7) which are housedin the main housing (8) and the planetary unit mounting plate, (9). Awheel (10) can be mounted on each pinion shaft which then meshes with asecond pinion (11). The pinion is connected to the planet carrier (12)via a spline connection that may be either a loose or shrink fit. Thepinion is supported on its other end by a bearing (13) housed in themain housing.

The geared generator module, (14), comprises a planetary gear unit and aflanged on or integrated generator (15). The module can be attached tothe planetary unit mounting plate via a flange (16). The planetary unitcomprises a rotating planet carrier, a stationary ring wheel (17) androtating planets (18). The sun shaft from the planetary stage, (19),drives the generator via a spline coupling and is supported by the meshon the one side and by the front generator bearing on the other.

In the construction shown in FIG. 3, the rotor is attached directly to aring wheel (20) that is supported by one large main bearing (21).Alternatively two main bearings may be used. The bearing is axiallyconstrained on the ring wheel by means of a split ring (22), and on it'souter diameter by part of the central bearing support plate, (23). Thering wheel drives several pinions (24) that are supported by twobearings, the first (25) which is housed in the front bearing supportplate (26) and the second (27) in the planetary unit mounting plate(28). (Note this is a variant of item (9) in FIG. 2)

The front support bearing for the pinion (30) driven by wheel (29) ishoused in the central bearing support that in turn is bolted to the mainhousing (31). The geared generator module can be identical in both ofthe constructions of FIGS. 2 and 3.

In both constructions, the main housing is fixed to the interface withthe rest of the wind turbine's structure via supports (32) that formpart of the main gearbox housing. The supports could be extended into amultifunctional “L” shaped base plate (33) that would support the gearunit and rotor as well as the yaw bearing (34) of the wind turbinenacelle.

Modularity is a significant aspect of the invention. By virtue ofmodularity the turbine rotor power is split at the first stage and formsindependent paths to the generators. This implies that the turbine couldoperate with as many of these paths as is desired. This would also bebeneficial in low wind situations or if one or more of the generatormodules is removed for maintenance. Furthermore, the modules could beused in different wind turbine sizes. This has logistical advantages forthe wind turbine manufacturer's service department.

A major advantage of splitting the rotor power into independent paths isthat there are no load sharing problems between the individual pinions.The loads are balanced by equalising the power delivered by thedifferent generators.

Integration is another important feature. Once assembled, the mainhousing could become part of the turbine structure and does not need tobe removed again. The unit is designed in such a way as to allow thedisassembly of all the gearbox internals. Furthermore, the wind turbinerotor bearings are integrated in the unit in both illustratedconstructional versions, enabling compact overall design, lower weightand cost saving.

In conventional designs a flexible coupling has the burden of taking upmisalignment between the generator shaft and gearbox HSS. In this designthe sun shaft is directly coupled to the generator using a splineconnection.

1-17. (canceled)
 18. A wind turbine gear unit comprising a low speedgear module and a plurality of high speed gear modules wherein said lowspeed gear module is operable simultaneously to transmit torque to eachof said high speed gear modules and whereby the rotor is supported by atleast one bearing which is integrated in the housing of the low speedgear module.
 19. The wind turbine gear unit according to claim 18,wherein at least one of said high speed gear modules is a multi-stagegear unit.
 20. The wind turbine gear unit according to claim 18, whereinsaid low speed gear module is a multi-stage gear unit.
 21. The windturbine gear unit according to claim 18, wherein the low speed gearmodule comprises a housing adapted to transfer rotor forces and bendingmoments to a nacelle structure.
 22. The wind turbine gear unit accordingto claim 21, wherein the housing is integrated with the base plate ofthe nacelle of the wind turbine.
 23. The wind turbine gear unitaccording to claim 22, wherein the housing is used to transmit rotorloads to a tower supporting the nacelle of the wind turbine.
 24. Thewind turbine gear unit according to claim 23, wherein the base plate ofthe nacelle incorporates a yaw bearing of the nacelle, allowing thenacelle to rotate on the tower.
 25. the wind turbine gear unit accordingto claim 24, wherein the housing is fixed to the wind turbine'sstructure via supports that form part of the housing and which areextended in a base plate that supports the gear unit and rotor, as wellas the yaw bearing of the nacelle.
 26. The wind turbine gear unitaccording to claim 18, wherein at least one of said high speed gearmodules comprises a support housing which is selectively releasable fromthe housing of the low speed gear unit.
 27. The wind turbine gear unitaccording to claim 18, wherein each high speed gear module housingprovides support for bearings which rotatably support one or morerotatable components of that gear module.
 28. The wind turbine gear unitaccording to claim 18, wherein at least one high speed gear module hasan electrical generator associated therewith.
 29. The wind turbine gearunit according to claim 28, wherein the or each said electricalgenerator receives input torque via only one high speed gear module. 30.The wind turbine gear unit according to claim 28, wherein a saidgenerator and associated high speed gear module form a sub-assemblywhich is selectively removable from the low speed gear module.
 31. Thewind turbine gear unit according to claim 30, wherein said generatorcomprises a shaft rotatably coupled to the high speed gear module via aspline connection.
 32. The wind turbine gear unit according to claim 18,wherein an intermediate stage gear module is provided between the lowspeed gear module and each high speed gear module.
 33. The wind turbinegear unit according to claim 18, wherein a spline connection is providedbetween the low speed gear module and each high speed gear module. 34.The wind turbine gear unit according to claim 18 and which is of anintegrated type in which a component of the low speed gear module actsas part of a main rotor bearing.
 35. The wind turbine gear unitaccording to claim 18, wherein the low speed shaft is supported on oneor more bearings which also act as rotor bearings.
 36. The wind turbinegear unit according to claim 18, wherein all modules are removablewhilst the housing is left in place to fulfill its structural role tosupport the rotor.
 37. The wind turbine gear unit according to claim 18,and substantially as hereinbefore described with reference to theaccompanying drawings.
 38. A wind turbine assembly comprising a windturbine gear unit according to claim 18, comprising a plurality ofelectrical generators and control means for selecting the number ofgenerators operable to generate electricity.
 39. A wind turbine assemblycomprising a wind turbine gear unit according to claim 18, a pluralityof electrical generators, a wind powered rotor assembly coupled to a lowspeed input of the low speed gear module, and a nacelle supportstructure, wherein the low speed gear unit comprises a housing whichtransmits forces from the rotor assembly to the nacelle supportstructure.
 40. A wind turbine assembly comprising a wind turbine gearunit according to claim 18, a plurality of electrical generators, a windpowered rotor assembly coupled to a low speed input of the low speedgear module, and a nacelle support structure mounted on a supportingtower, wherein the low speed gear unit comprises a housing whichtransmits forces from the rotor assembly to the tower.
 41. A windturbine assembly comprising a wind turbine gear unit comprising a lowspeed gear module and a plurality of high speed gear modules to drive aplurality of generators, wherein said low speed gear module is operablesimultaneously to transmit torque to each of said high speed gearmodules; a wind powered rotor assembly coupled to a low speed input ofthe low speed gear module; and a nacelle support structure with a baseplate incorporating a yaw bearing for mounting the nacelle on a tower,wherein the low speed gear unit comprises a housing that is integratedwith the base plate of the nacelle.